The accurate proportioning of chemicals into pressurized flowing conduits is required in many applications. In agriculture, additives such as pesticides, herbicides and fertilizers are directly injected at various proportions into crop irrigation systems. Flow rates and pressures may continually change in the pipelines as sprinklers are turned on or off, or as elevations and pumping conditions change. Providing large amounts of power to drive an injection pump at remote sites may be difficult as well. In firefighting applications, a foam concentrate is injected into fire hoses at specific proportions so that proper foaming from the fire nozzles is achieved. Flow rates and pressures in the water lines are continually changing as firefighters adjust nozzles, add more hoses, increase fire pump pressure, etc.
One method of proportioning fluids into pressurized pipelines is exemplified by the U.S. Pat. No. 5,494,112 to Arvidson et al. This system injects firefighting foam concentrate into water streams that are intended to put out fires. A positive displacement pump at a given speed delivers a fixed volume of foam concentrate. The flow rate in the conduit into which the foam concentrate is to be injected is measured by a flowmeter which is inserted into the flowing conduit. This signal is then electronically manipulated and used to adjust the speed of the positive displacement pump to deliver the proper proportion of injected fluid to conduit fluid (water). Problems with these types of systems include damage to the flowmeter by debris flowing in the conduit, and inability to compensate for large changes in the pressure within the conduit. In addition, for high flow rates of the proportioned fluid, significant power is required to drive the positive displacement pump, which creates a substantial power draw on the fire truck electrical system.
Diaphragm pumps have been used for pumping fluids. For example, U.S. Pat. No. 3,250,226 to Voelker and U.S. Pat. No. 3,749,526 to Ferrentino disclose the concept of two hydraulically connected diaphragm chambers which are pressurized and depressurized to provide continuous pumping action. However, these systems are not capable of proportioning fluids into systems flowing with a second fluid where flow rates and/or pressures are varying in the second fluid.
U.S. Pat. No. 5,009,244 to Grindley et al. illustrates an example of a system that includes a vessel with a diaphragm for proportioning. The device disclosed in that patent provides proportioning of one fluid into another fluid and is not affected by pressure changes. However, because it has only one diaphragm vessel, the device must be stopped to be refilled with the fluid to be injected, and thus is not able to automatically and continuously proportion fluid. For systems which require large flow rates of the proportioned fluid, the device must be stopped fiequently or a very large vessel must be provided. Because large pressure vessels can be bulky, heavy and expensive and may require ASME coding, such systems are impractical for situations requiring large flow rates or proportioning for an extended period of time.